Conventionally, a polyimide resin or benzoxazole resin excellent in all of heat resistance, electric properties, mechanical properties, etc., is widely used for the surface protective film and interlayer insulating film employed in a semiconductor device. These resins exhibit low solubility in various solvents and therefore, are generally used as a composition after the resin in the form of a precursor prepared by ring-opening the cyclic structure is dissolved in a solvent. Accordingly, a step of ring-closing the precursor is required when using the resin. This ring-closing step is usually carried out by heat curing under heating at 300° C. or more.
However, in recent years, a semiconductor device inferior in the heat resistance compared with conventional products is being developed and in turn, lowering the heat curing temperature is required of the material for forming a surface protective film or an interlayer insulating film, as a result, the demand for heat curing at 300° C. or less, or furthermore, heat curing at 250° C. or less is increasing.
To meet such a requirement, Patent Document 1 has proposed a photosensitive resin composition excellent in the photosensitive performance, containing, as the base resin, a phenolic hydroxyl group-containing alkali-soluble resin that is widely used as the base resin in the resist field, and furthermore, containing a quinone diazide compound and a curing agent, and it is disclosed that this photosensitive resin composition is heat-cured by heating at a temperature of 100 to 250° C. for 30 minutes to 10 hours.
Patent Document 2 also proposes a photosensitive resin composition containing a novolak resin that uses a phenol compound having a benzene nucleus containing two or more hydroxyl groups and has a weight average molecular weight of 1,000 to 20,000, and a photosensitizing agent.
In addition, Patent Document 3 has proposed a reactive resin composition using a resin having, in the skeleton, a condensation product of a biphenyl compound with phenols, and using a photopolymerization initiator and/or a photoacid generator, which is a material excellent in electrical properties and usable for forming a liquid crystal alignment-controlling bump and/or a spacer or forming a liquid crystal alignment-controlling bump and a spacer at the same time, and it is disclosed that this reactive resin composition is heat-cured by heating at a temperature of 150 to 400° C. for 10 to 120 minutes.